IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 09, 2015 | ISSN (online): 2321-0613
Studies on Impact Strength of Concrete with Nano-Materials at Elevated Temperatures A. Narender Reddy1 D. Ramesh2 M.Tech Student 2Assistant Professor 1,2 Department of Civil & Structural Engineering 1,2 Newton’s Institute of Science and Technology, Macherla, Guntur District, Andhra Pradesh, India 1
Abstract— Nano composites are produced by adding nanoparticles to a material in order to improve the properties of material. Concrete is a material most widely used in construction industry. Concrete is a composite material made up of cement, sand, aggregate, water and mineral or chemical admixtures. The materials such as nano-silica, nano flyash, nano metakaolin are being combined with cement. There are also a limited number of investigations dealing with the manufacture of nano-cement. The use of finer particles (higher surface area) has advantages in terms of filling the cement matrix, densifying the structure, resulting in higher strength and faster chemical reactions i.e. hydration reactions. Nano-cement particles can accelerate cement hydration due to their high activity. Similarly, the incorporation of nano-particles can fill pores more effectively to enhance the overall strength and durability. Normally, the particle size ranges between 1nm to100nm, they are generally called as nano materials. The fineness can reach up to molecular level by special processing techniques. An experimental investigation has been carried out to determine the influence of concrete with nano-cement particles under elevated temperature. M20, M30 and M40 grades of concrete were cast. For each of grades of concrete, 10%, 20% and 30% of cement was replaced with nanocement. The particle size of nano-cement was determined using a Scanning Electron Microscope (SEM). Impact strength of concrete with nano materials under various elevated temperature (250°C, 500°C, 750°C and 1000°C) were found by using Impact Testing Apparatus. Impact strength is found to be least for the concrete specimens with 30% replacement of nano-cement. It was also found that impact strength of M40 grade concrete specimens was low as compared to other grades of concrete (M20 & M30). Key words: Nano-Materials, Casing of concrete I. INTRODUCTION Concrete is a composite material composed mainly of water, aggregate, and cement. Often, additives and reinforcements are included in the mixture to achieve the desired physical properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily molded into shape. Concrete has relatively high compressive strength, but significantly lower tensile strength, and as such is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develop. Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete which is subjected to long-duration forces is prone to creep. In very high-strength concrete mixtures (greater than 70 MPa) the crushing strength of the aggregate can be a limiting factor to the
ultimate compressive strength. The effect of fire on building members has an important role in the construction. The thermal behavior of the members subjected to temperature loads will give an over view about how they react with temperature. The field quality of fire protection materials is now getting deserved attention. It is a positive trend that engineers work with fire engineers to protect the structures, and the responsibility for fire-resistant design is delegated to the structural engineers. Due to the increased incidents of major fires in buildings; assessment, repairs and rehabilitation of fire-damaged structures has become a topical interest. This is a specialized field involves expertise in many areas like concrete technology, material science and testing, structural engineering, repair materials etc. Research and developmental efforts are being carried out in this area and other related disciplines. The reinforced concrete is the one of the most widely using construction material, and the fire will affect the members very badly in the form of spalling, exposing of reinforcement etc. The structural property of concrete that has been most widely studied as a function of temperature exposure is compressive strength. In buildings, structural members are to satisfy fire resistance ratings prescribed in building codes. Fire resistance is the duration during which a structural member exhibits resistance with respect to strength, integrity and stability and depends on many factors including structural geometry, material used in construction and characteristics of fire. A fire resistance rating is the fire resistance of a member rounded off to nearest hour or half-hour. Concrete due to its low thermal conductivity, high thermal capacity and slower loss of strength and stiffness properties performs reasonably well under fire. Therefore, concrete structures are often used without any fire protection. It is necessary to understand the behaviors of structural elements subjected to fire. Although extensive experimental investigations and theoretical analyses have been conducted on structural materials and elements exposed to elevated temperature, to date, there are still many outstanding issues which have not been understood due to the complexity of structural fire resistance properties and the limitation of testing technique. At present, the fire-resistant design of most buildings is primarily based on these concepts resulting from the conventional design at room temperature or the previous simple test results. In practice, the design method with the help of detailing is still a main fire-resistant design method. Nearly all collapses in fire-damaged concrete structures are caused either by poor detailing or, in severe cases, by failure of the steel reinforcement. This is because the reinforcement is usually placed near the concrete member surface. Hence, the reinforcement is subjected to a greater temperature increase, and its strength is first affected in comparison to the main body of concrete. fineness increases, the surface area increases, which increases the ‘reactivity’ of the
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